This invention relates to tackifier resin compositions for use in adhesives and to methods for their preparation. More particularly, this invention relates to light colored tackifier resin compositions prepared from piperylene concentrate and vinyl aromatic monomers and their use in adhesive applications.
Tackifier resins can be used for making thermoplastic adhesives such as hot melts and pressure sensitive adhesives. The adhesives are made of elastomers, block copolymers, ethylene vinyl acetate (EVA), or amorphous polyolefins along with low molecular weight oligomer tackifiers. A common tackifier is made of aliphatic petroleum hydrocarbon feedstocks from ethylene crackers in the oil refinery, using cationic polymerization.
In the industry, C.sub.5 resins are commonly made from piperylene concentrates using AlCl.sub.3 catalyst at 30.degree.-50.degree. C. These resins have a softening point from 60.degree.-120.degree. C. with a Gardner color from about 4-6. Dark color and poor heat stability of the C.sub.5 resins limit applications and there is a need for light color resins. Therefore, the hydrogenated product from aromatic petroleum resin or styrene modified terpene resins are commonly employed for light colored adhesives.
U.S. Pat. No. 4,046,838 discloses a composition of a mixture of (i) an unvulcanized elastomeric block copolymer having the structure A--B--A where A is a nonelastomeric styrene block polymer and B is an elastomeric diene block polymer of 1,3 butadiene and (ii) tackifying resin derived from piperylene. The resin of this patent has Gardner colors greater than 4. U.S. Pat. No. 3,872,064 discloses a hydrocarbon derived resin prepared from the polymerized mixture of a piperylene tackifier in the presence of boron trifluoride (BF.sub.3) catalyst. The Gardner color of the resins in this patent is about 4. U.S. Pat. No. 3,853,826 discloses a hydrocarbon derived resin derived from piperylene using a catalyst of boron trifluoride (BF.sub.3) together with a boron trifluoride ether complex. This resin has Gardner colors in the range of 2 to 8 and narrow molecular weight distribution. U.S. Pat. Nos. 4,189,547, 4,098,983, and 3,287,332 also disclose hydrocarbon derived resins using a petroleum fraction such as piperylene as a tackifier.
Thermoplastic adhesives can be prepared from elastomers such as block copolymers, oil and tackifiers. These adhesives can be prepared using solvent or by hot melt techniques. Depending on the room temperature tackiness, thermoplastic adhesives can be divided into pressure sensitive adhesives (PSA) and hot melt adhesives. PSA are tacky at room temperature with applications as tape and label adhesives. Hot melt adhesives are not tacky at room temperature and have applications as bookbinding and box closing adhesives.
Hot melt adhesives used for bonding in a particular use or application may be completely unsuitable for other uses or applications. Depending upon the type of construction employed, the adhesive must possess certain physical properties. Perhaps the most stringent properties are those required for adhesives to be used in the bonding of polyethylene films, or the like, to tissue or non-woven substrates in the production of articles, particularly diapers, sanitary napkins and bed pads. Using multi-line construction presents unique problems for the adhesive formulator. The adhesive should possess a high degree of tackiness, since it is applied in the form of very fine parallel longitudinal stripes, thus requiring each line of adhesive to possess exceptionally high bonding properties. The adhesive should also possess sufficient adhesive and cohesive strength to provide high bond strength values when subjected to stress so the contructions cannot be easily separated. As an additional criteria, it is necessary that the adhesive, upon application, not be absorbed throughout the actual disposable construction and that the adhesive bonds not only remain secure but also be flexible even after prolonged periods of storage. In addition to requiring heat and oxidation resistance on aging, they should also possess sufficient bonding range and should be white or clear in color. Recently, hot melt pressure sensitive technology has been developed for non-woven adhesive applications, specifically for diaper adhesives.
U.S. Pat. No. 4,526,577 discloses how to prepare hot melt pressure sensitive adhesives for non-wovens from tackifier resins and block copolymers, specifically multiblock SB and SIS block copolymers. Tackifiers such as C.sub.5, styrenated terpenes, cycloaliphatic resins and hydrogenated hydrocarbon resins are employed for hot melt pressure sensitive adhesives. The requirements for the adhesives are stringent in that they should have good adhesion onto polyethylene and non-woven substrates. In addition, hot melt pressure sensitive adhesives are currently being applied by spray techniques at 275.degree.-350.degree. F. requiring good rheological properties at the melt stage.
Prior to the present invention, adhesive compositions using piperylene resins as a tackifier normally had dark color and poor color and viscosity stability upon heat aging. The PSA adhesive compositions also have unbalanced adhesive and cohesive strengths for hot melt applications. Hence, these adhesive compositions had a limited use on a commerical basis.
None of the above mentioned prior art discloses the instant invention.